Relationship between age at initiation of cysteamine treatment, adherence with therapy, and glomerular kidney function in infantile nephropathic cystinosis.

Infantile nephropathic cystinosis, due to impaired transport of cystine out of lysosomes, occurs with an incidence of 1 in 100-200,000 live births. It is characterized by renal Fanconi syndrome in the first year of life and glomerular dysfunction progression to end-stage kidney disease by approximately 10 years of age. Treatment with oral cysteamine therapy helps preserve glomerular function, but affected individuals eventually require kidney replacement therapy. This is because glomerular damage had already occurred by the time a child is diagnosed with cystinosis, typically in the second year of life. We performed a retrospective multicenter study to investigate the impact of initiating cysteamine treatment within the first 2 months of life in some infants and comparing two different levels of adherence in patients diagnosed at the typical age. We collected 3983 data points from 55 patients born between 1997 and 2020; 52 patients with 1592 data points could be further evaluated. These data were first analyzed by dividing the patient cohort into three groups: (i) standard treatment start with good adherence, (ii) standard treatment start with less good adherence, and (iii) early treatment start. At every age, mean estimated glomerular filtration rate (eGFR) was higher in early-treated patients than in later-treated patients. Second, a generalized additive mixed model (GAMM) was applied showing that patients with initiation of treatment before 2 months of age are expected to have a 34 ml/min/1.73 m2 higher eGFR than patients with later treatment start while controlling for adherence and patients' age. These data strongly suggest that oral cysteamine treatment initiated within 2 months of birth preserves kidney function in infantile nephropathic cystinosis and provide evidence of the utility of newborn screening for this disease.

Interferon-driven brain phenotype in a mouse model of RNaseT2 deficient leukoencephalopathy.

Infantile-onset RNaseT2 deficient leukoencephalopathy is characterised by cystic brain lesions, multifocal white matter alterations, cerebral atrophy, and severe psychomotor impairment. The phenotype is similar to congenital cytomegalovirus brain infection and overlaps with type I interferonopathies, suggesting a role for innate immunity in its pathophysiology. To date, pathophysiological studies have been hindered by the lack of mouse models recapitulating the neuroinflammatory encephalopathy found in patients. In this study, we generated Rnaset2-/- mice using CRISPR/Cas9-mediated genome editing. Rnaset2-/- mice demonstrate upregulation of interferon-stimulated genes and concurrent IFNAR1-dependent neuroinflammation, with infiltration of CD8+ effector memory T cells and inflammatory monocytes into the grey and white matter. Single nuclei RNA sequencing reveals homeostatic dysfunctions in glial cells and neurons and provide important insights into the mechanisms of hippocampal-accentuated brain atrophy and cognitive impairment. The Rnaset2-/- mice may allow the study of CNS damage associated with RNaseT2 deficiency and may be used for the investigation of potential therapies.

Targeted metabolomics revealed changes in phospholipids during the development of neuroinflammation in Abcd1tm1Kds mice and X-linked adrenoleukodystrophy patients.

X-linked adrenoleukodystrophy (X-ALD) is the most common leukodystrophy. Despite intensive research in recent years, it remains unclear, what drives the different clinical disease courses. Due to this missing pathophysiological link, therapy for the childhood cerebral disease course of X-ALD (CCALD) remains symptomatic; the allogenic hematopoietic stem cell transplantation or hematopoietic stem-cell gene therapy is an option for early disease stages. The inclusion of dried blood spot (DBS) C26:0-lysophosphatidylcholine to newborn screening in an increasing number of countries is leading to an increasing number of X-ALD patients diagnosed at risk for CCALD. Current follow-up in asymptomatic boys with X-ALD requires repetitive cerebral MRIs under sedation. A reliable and easily accessible biomarker that predicts CCALD would therefore be of great value. Here we report the application of targeted metabolomics by AbsoluteIDQ p180-Kit from Biocrates to search for suitable biomarkers in X-ALD. LysoPC a C20:3 and lysoPC a C20:4 were identified as metabolites that indicate neuroinflammation after induction of experimental autoimmune encephalitis in the serum of Abcd1tm1Kds mice. Analysis of serum from X-ALD patients also revealed different concentrations of these lipids at different disease stages. Further studies in a larger cohort of X-ALD patient sera are needed to prove the diagnostic value of these lipids for use as early biomarkers for neuroinflammation in CCALD patients.

Mesenchymal Hamartoma of the Liver and DICER1 Syndrome.

Mesenchymal hamartoma of the liver (MHL) is a benign tumor affecting children that is characterized by a primitive myxoid stroma with cystically dilated bile ducts. Alterations involving chromosome 19q13 are a recurrent underlying cause of MHL; these alterations activate the chromosome 19 microRNA cluster (C19MC). Other cases remain unexplained. We describe two children with MHLs that harbored germline DICER1 pathogenic variants. Analysis of tumor tissue from one of the children revealed two DICER1 "hits." Mutations in DICER1 dysregulate microRNAs, mimicking the effect of the activation of C19MC. Our data suggest that MHL is a new phenotype of DICER1 syndrome. (Funded by the Canadian Institutes of Health Research and others.).

From ventriculomegaly to severe muscular atrophy: expansion of the clinical spectrum related to mutations in AIFM1.

The apoptosis-inducing factor (AIF) functions as a FAD-dependent NADH oxidase in mitochondria. Upon apoptotic stimulation it is released from mitochondria and migrates to the nucleus where it induces chromatin condensation and DNA fragmentation. So far mutations in AIFM1, a X-chromosomal gene coding for AIF, have been described in three families with 11 affected males. We report here on a further patient thereby expanding the clinical and mutation spectrum. In addition, we review the known phenotypes related to AIFM1 mutations. The clinical course in the male patient described here was characterized by phases with rapid deterioration and long phases without obvious progression of disease. At age 2.5 years he developed hearing loss and severe ataxia and at age 10 years muscle wasting, swallowing difficulties, respiratory insufficiency and external opthamoplegia. By next generation sequencing of whole exome we identified a hemizygous missense mutation in the AIFM1 gene, c.727G>T (p.Val243Leu) affecting a highly conserved residue in the FAD-binding domain. Summarizing what is known today, mutations in AIFM1 are associated with a progressive disorder with myopathy, ataxia and neuropathy. Severity varies greatly even within one family with onset of symptoms between birth and adolescence. 3 of 12 patients died before age 5 years while others were still able to walk during young adulthood. Less frequent symptoms were hearing loss, seizures and psychomotor regression. Results from clinical chemistry, brain imaging and muscle biopsy were unspecific and inconsistent.

Initial insight into the function of the lysosomal 66.3 kDa protein from mouse by means of X-ray crystallography.

BACKGROUND: The lysosomal 66.3 kDa protein from mouse is a soluble, mannose 6-phosphate containing protein of so far unknown function. It is synthesized as a glycosylated 75 kDa precursor that undergoes limited proteolysis leading to a 28 kDa N- and a 40 kDa C-terminal fragment. RESULTS: In order to gain insight into the function and the post-translational maturation process of the glycosylated 66.3 kDa protein, three crystal structures were determined that represent different maturation states. These structures demonstrate that the 28 kDa and 40 kDa fragment which have been derived by a proteolytic cleavage remain associated. Mass spectrometric analysis confirmed the subsequent trimming of the C-terminus of the 28 kDa fragment making a large pocket accessible, at the bottom of which the putative active site is located. The crystal structures reveal a significant similarity of the 66.3 kDa protein to several bacterial hydrolases. The core alphabetabetaalpha sandwich fold and a cysteine residue at the N-terminus of the 40 kDa fragment (C249) classify the 66.3 kDa protein as a member of the structurally defined N-terminal nucleophile (Ntn) hydrolase superfamily. CONCLUSION: Due to the close resemblance of the 66.3 kDa protein to members of the Ntn hydrolase superfamily a hydrolytic activity on substrates containing a non-peptide amide bond seems reasonable. The structural homology which comprises both the overall fold and essential active site residues also implies an autocatalytic maturation process of the lysosomal 66.3 kDa protein. Upon the proteolytic cleavage between S248 and C249, a deep pocket becomes solvent accessible, which harbors the putative active site of the 66.3 kDa protein.